From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

Oil discharged from an ocean-going tanker, pipeline, or oil installation, often as a result of damage. An oil spill kills shore life, clogging the feathers of birds and suffocating other creatures. At sea, toxic chemicals spread into the water below, poisoning sea life. Mixed with dust, the oil forms globules that sink to the seabed, poisoning sea life there as well. Oil spills are broken up by the use of detergents but such chemicals can themselves damage wildlife. The annual spillage of oil is 8 million barrels (280 million gallons) a year. At any given time tankers are carrying 500 million barrels (17.5 billion gallons).

The amount of oil entering oceans from shipping operations decreased by 60% 1981–91.

In March 1989 the Exxon Valdez (belonging to the Exxon Corporation) ran aground and spilled oil in Alaska's Prince William Sound, covering 12,400 sq km/4,800 sq mi and killing at least 34,400 sea birds, 10,000 sea otters, and up to 16 whales. The incident led to the US Oil Pollution Act of 1990, which requires tankers operating in US waters to have double hulls.

The world's largest oil spill was in the Gulf in 1991 as a direct result of hostilities during the Gulf War. Around 6–8 million barrels (210–280 million gallons) of oil were spilled, polluting 675 km/420 mi of Saudi coastline. In some places, the oil was 30 cm/12 in deep in the sand.

In the Niger River delta in Nigeria, Shell pipelines have repeatedly burst; in 1970 oil spilled across an area of 8 sq km/3 sq mi, which remained contaminated for over 20 years.

In December 1989, an Iranian tanker leaked 19 million gallons off the coast of Morocco. In 1994, in the Komi region of north Russia, a broken pipeline leaking into the Pechora River was estimated to have caused one of the biggest oil spills since 1989.

In February 1996, the Norwegian tanker the Sea Empress ran aground near the entrance to Milford Haven harbour, Wales, UK, letting loose a flood of 19.5 million gallons of crude oil. The port authority responsible for this oil spill, which devastated fishing, wildlife, and tourism in west Wales, was fined £4 million in January 1999, the largest penalty for causing pollution in British legal history.

Over one million gallons of crude oil leaked into the Iguaçu River in southwest Brazil in July 2000. It came from an underwater pipeline at a state-operated oil refinery, Petrobras, and was Brazil's worst oil spill for 25 years. Petrobras was fined US$110 million.

An oil slick from a stranded tanker threatened rare wildlife on Ecuador's Galapagos Islands in January 2001. About 80% of the 24,000-gallon cargo leaked into the sea. Ecuador declared a state of emergency and appealed for international assistance to fund a clean-up. Winds and shifting ocean currents helped disperse the oil.